Texas Instruments MSP430x1xx manual Writing Flash Memory, 2. Write Modes, Byte/Word Write

Flash Memory Operation

5.3.3Writing Flash Memory

The write modes, selected by the WRT and BLKWRT bits, are listed in

Table 5−1.

Table 5−2. Write Modes

BLKWRT	WRT	Write Mode
0	1	Byte/word write
1	1	Block write

Both write modes use a sequence of individual write instructions, but using the block write mode is approximately twice as fast as byte/word mode, because the voltage generator remains on for the complete block write. Any instruction that modifies a destination can be used to modify a flash location in either byte/word write mode or block write mode.

The BUSY bit is set while a write operation is active and cleared when the operation completes. If the write operation is initiated from RAM, the CPU must not access flash while BUSY=1. Otherwise, an access violation occurs, ACCVIFG is set, and the flash write is unpredictable.

Byte/Word Write

A byte/word write operation can be initiated from within flash memory or from RAM. When initiating from within flash memory, all timing is controlled by the flash controller, and the CPU is held while the write completes. After the write completes, the CPU resumes code execution with the instruction following the write. The byte/word write timing is shown in Figure 5−7.

Figure 5−7. Byte/Word Write Timing

	Programming Operation Active
Generate		Remove
Programming Voltage		Programming Voltage

BUSY

Programming Time, VCC Current Consumption is Increased

tWord = 35/fFTG

When a byte/word write is executed from RAM, the CPU continues to execute code from RAM. The BUSY bit must be zero before the CPU accesses flash again, otherwise an access violation occurs, ACCVIFG is set, and the write result is unpredictable.

5-8 Flash Memory Controller